Single wafer plasma etchers are known in the art. Plasma etchers include a reactor chamber, a susceptor or electrostatic chuck in the reactor chamber, and a top electrode in the reactor chamber, above the electrostatic chuck. A wafer is supported on the electrostatic chuck, etching gasses are introduced into the reactor chamber, and a plasma is initiated by supplying a voltage between the top electrode and the electrostatic chuck. It is known to employ stacked plasma confinement rings in single wafer plasma etchers. A plasma confinement ring is an annular ring made of SiO.sub.2 that is positioned intermediate the electrostatic chuck and the top electrode in the reactor chamber of a single wafer plasma etcher. The ring has upper and lower opposite surfaces, and has a central aperture including a vertical annular surface. The central aperture has a diameter which is just slightly larger than the diameter of the wafer. The opening in the ring focuses or centralizes the plasma over the wafer for etching purposes.
In the course of the plasma etching, and particularly when using a perfluorocarbon or hydrofluorocarbon etching gas chemistry, gas fragments condense on interior chamber surfaces and react to form short-chain "polymers." These polymers become especially thick on the interior vertical surface of the central aperture of the ring. This surface sees much more of the plasma than the upper and lower flat surfaces because plasma formed in the reactor is more concentrated against this vertical surface than upper and lower surfaces of the ring.
The polymer or precursor continues to build until the point where it must be cleaned from the surfaces. If it is not cleaned soon enough, it starts to peel or flake-off and fall and deposit either on the wafer (creating point defects) or on the electrostatic chuck, preventing adhesion of subsequent wafers to the chuck, thereby halting the process. It may also deposit on a wafer in process, leading to manufacturing defects and yield loss. The manufacturers of such plasma reactors and rings have procedures and processes as to how to clean the ring after the polymer or precursor is formed. One plasma etching apparatus, employing confinement rings, is described in U.S. Pat. No. 5,534,751 to Lenz et al.
Fairly sharp edges or corners are defined where the annular surface meets the upper and lower surfaces of the ring, although these corners are slightly rounded due to the process of manufacture or for safety reasons. The inventors of the present invention have discovered that these sharp edges define "delamination initiation corners" which throughout the course of heat cycling or temperature cycling creates a stress point in the deposited polymer or precursor film which facilitates interfacial crack propagation causing it to flake off the ring.